System for pumping slurry or gel explosives into boreholes



1968 T. K. COLLINS ET AL 3,361,023

SYSTEM FOR PUMPING SLURRY OR GEL EXPLOSIVBS INTO BOREHOLES Filed July28, 1966 x .k w o j V .5; INVENTORS s THOMAS K comm/s ROBERT 5. 04A) 45x4. war d 0 IO 20 30 4O .50 60 TIME SECONDS United States Patent3,361,023 SYSTEM FOR PUMPING SLURRY 0R GEL EXPLOSIVES INTO BOREHOLESThomas K. Collins, Salt Lake City, Robert B. Clay, Bountlful, and Lex L.Udy, Salt Lake City, Utah, assignors to Intermountain Research andEngineering Company, a corporation of Utah Filed July 28, 1966, Ser. No.568,642 12 Claims. (CI. 8620) ABSTRACT OF THE DISCLOSURE Since theintroduction of slurry explosives, such as those described in US. Patent2,930,685 and Re. 25,695 by Cook and Farnam, these materials have foundincreasing utility, particularly in the blasting of hard rock, such astaconite, other iron ores, and the like. It is often difficult, however,to control the placement of these slurries in the blasting site, andparticularly in waterfilled boreholes. By water-filled boreholes it isintended to mean holes containing liquid water in quantity. In a typicalsituation, in hard rock blasting, a hole may be bored from five to fortyor more feet in depth, with a diameter which may be as small as 2 or 3inches but is more usually from 6 to 10 inches, or even larger. Holes ofthe larger sizes are usually spaced at suitable intervals in twodirections, the spacing depending on the strength of the explosive andthe type of rock being blasted, the degree and kind of breakage desired,etc. A typical spacing is often about 20 to 25 feet in each of twohorizontal directions. Large quantities of explosive may be placed ineach borehole to fill them to a depth ranging from a few feet to 20 or30 feet or more. A number of charges may be detonated simultaneously.

As is now well known in the art, these slurry or gel liquid orsemiliquid materials are relatively insensitive and quite safe tohandle. Preferably, they are pumpable, that is they flow like viscousliquids, and are often and preferably mixed right on site and pumpeddirectly from the mixing operation into the borehole or blasting point.In fact, the pumping of a gel or slurry through a hose or other deliverytube may be an effective continuation of the mixing, since there is acertain amount of shear and intermixing of the ingredients occurring inthe slurry as it passes through a conduit. The latter may be a pipe butis usually a flexible hose. However, the materials may be premixed andmay be simply forced through the delivery conduit, e.g. a hose, directlyinto the borehole of the mine.

The pumping of such slurry or gel explosives from a mixing or supplystation directly into a borehole involves several problems. The blastingcompositions are sufliciently viscous to prevent substantialgravitational segre gation of suspended articles from the liquid orsemiliquid menstruum or continuous phase. However, they must not be tooviscous to be pumped; on the other hand, once they are in the hole theyshould not be so liquid that the undissolved components will separate onstanding, even on standing for prolonged periods of time.

These slurries, or gels, the terms being synonymous for purposes of thisinvention, usually contain a thickening agent. Preferably the thickeningagent is one which is adequate to prevent serious segregation of theslurry in the hose or conduit but does not become fully effective in itsthickening or viscosity increasing function until the material is in theborehole. This thickening agent may be a simple gelling agent such as agum, a flour, a starch, or it may be a gelling agent plus across-linking agent such as sodium or potassium dichromate, borax, orthe like. Numerous cross-linking agents are known that are useful. Thegelling agent may be either a starchtype thickener, such as wheat flour,tapioca flour, potato starch, etc., or a galactomannin material such asguar gum, or locust bean gum, methyl cellulose, or various otherthickeners which are known. In general, the starches and the guar gumare preferred, and mixtures of the materials named above may be used. Asis well known in the art, the required amount of thickener dependsconsiderably on the type of material being thickened, the temperature atwhich it is mixed and used, etc. Typically, guar gum proportions may befrom 0.05 to 1% or more, and for starches they may be as high as 5 or6%. A more typical figure is about 0.5% of thickener when guar gum isused, or 2 to 4% when a material such as tapioca starch is used as athickener. While water is the least expensive solvent or menstruum,other liquid materials may be added or substituted, wholly or in part.It is often desirable to use small proportions of organic liquids, suchas alcohols, glycols, glycol ethers, formamide and its alkylatedderivatives and the like, along with water.

For best results, particularly in water-filled boreholes, the slurryshould be denser than the water, so that it will settle or rest at thebottom and not float in water. Thus it may have a density of as littleas about 1.05 to as much as about 1.8 or more grams per cubiccentimeter. A typical slurry of a kind presently preferred has a densitybetween about 1.15 and 1.4 grams per cc., but may be well outside theselimits if desired. In any case, for the purposes of the presentinvention, it should be at least a little denser than water and itshould have fairly high water resistance. That is to say, it should notreadily be penetrated or leached, even if there is water running throughthe borehole. The gel or slurry, when it reaches the borehole, shouldhave some structure or water resistance due to the thickener. It shouldnot break up and allow segregation of insoluble components, such asparticulate fuels and sensitizers, e.g. particles of metallic aluminum,or of undissolved ammonium nitrate, sodium nitrate, or other inorganicnitrates, chlorates, or perchlorates, or particles of sulfur,carbonaceous particles such as coal or gilsonite, or the like. Any orall of these, or various combinations of two or more of them, may beused in suitable proportions, as is now well known in the art.

Instead of using a pump, a pressure vessel and a supply of compressedair or other fluid may be used to force the slurry through the deliveryhose or tube. With a long hose, or one of relatively small diameter,considerable pressure may be required. Hoses may be as small as 1%inches in diameter and up to several hundred feet long. Pressures ashigh as to lbs. p.s.i. and more, have been used in some cases to forceslurry material into the borehole. Preferably, hoses of larger diameterare used, e.g. 1 /2 to 2 /2 inches or more, to reduce pressurerequirements. Blasting slurries and gel may be quite thick, even withouta gelling agent but it is preferable to use materials which, at the timeof pumping, and as they pass through the hose, are sufliciently fluidthat they can be pumped into place with moderate pressures at the pump.It is desirable to be able to pump at pressures which do notsubstantially exceed about 30 to 40 p.s.i. and it is preferable to usematerials which can be pumped at 5 to pounds p.s.i., if their componentsdo not segregate too readily. It is much easier to handle the hose,there is less danger of hose whipping or bursting, or of accidentalexplosion. When driving the material through the hose pressures up to100 to 150 p.s.i. or more, which has sometimes been done, the hosebecomes very difiicult to handle. It will sometimes force itself out ofthe borehole, even against the holding of one or two strong men, and mayspray the explosive material all over the area, and onto the menthemselves, with possible serious hazards.

For all these reasons it is preferred to use a mix of low viscosityconsistent with stability. A mixture is prepared which has the necessaryoxidizer ingredients such as ammonium nitrate, sodium nitrate, and/orchlorates, perchlorates and the like, along with appropriate fuelsand/or sensitizers such as powdered aluminum, finely divided coal orgilsonite, sulfur and, including in some cases self-explosive materialspreviously mentioned, such as particulate TNT, smokeless powder and thelike. These may be used sometimes without a gelling agent, when theystabilize against segregation, but it is usually pre ferred to add adelayed action thickener.

A thickening agent should be used which does not increase viscosity sogreatly as to interfere with pumping at reasonable pressures. It shouldbe effective to prevent serious segregation in the flow line, if thereis a tendency to segregation. As the material reaches the borehole, itshould thicken up sufiiciently to prevent substantial segregation ofsuspended particles and erosion of gel structure even after longstanding and in the presence of liquid water.

It is preferable to use a water-resistant thickening or gelling agent.For this purpose, a material such as tapioca flour or guar gum, or amixture of the two, may be employed along with a cross-linking materialor activator to expedite and augment the thickening effect and tominimize the amount of thickening agent required.

In a typical operation, a slurry made up of a liquid, usually aconcentrated or saturated solution of an oxidizer salt, is blended in amixer with dry ingredients which are either insoluble or only partlysoluble in the liquid, under the conditions. The resulting slurry isimmediately pumped or forced by pneumatic pressure through a hose orother conduit to the borehole, cavity, or point of use, the wholeoperation taking usually less than a minute-sometimes only a fewseconds. It is essential then that the material be suitable inconsistency and viscosity to flow under reasonable pressure through thehose, but it preferably increases in viscosity on arriving in the site,being sufficiently gelled or thickened within to 30 or up to 60 secondsor so, that (a) the suspended non-dissolved particles will not separatefrom the liquid suspending medium in the borehole and (b) the gel willnot break down on standing, even in the presence of water. Hence thetiming or predetermination of the rate of thickening or gelling isusually very important. A thickener of known properties, such asprecooked starch, tapioca flour, etc., or a guar gum, combined with anactivator, or accelerator or cross-linking agent of known properties,can be used to get the consistency or structure desired at the timerequired.

Since the use of a cross-linking agent is often highly desirable, oneshould be chosen that will give the desired results with reasonablecertainty. For purposes of this in.- vention the dichromates such assodium or potassium dichromate, mentioned above, are particularlydesirable. With them a relatively thin slurry which is easy to pump canbe fed into the delivery hose, and have good resistance against waterleaching or penetration by the time the explosive strikes the water inthe borehole, even though the slurry is still quite a thin and pumpableor fluid gel in structure.

Turning now to mechanical considerations, as a rule pumps ofconsiderable capacity are used since it is desirable to fill theboreholes rather rapidly for efiiciency of operation. The use of suchpumps frequently may tend to introduce undesirable quantities of airinto the gel. While a small proportion of air may not be objectionable,and may be even beneficial, it is undesirable to allow the pump to beatlarge quantities of air into the material. In particular, the processshould be so controlled that air in large bubbles or gulps is notintroduced into the charge. Such large bubbles may rise through theslurry in a water filled borehole and mix water into it in substantialamounts. To cause mixing at the water-slurry interface may be verydetrimental. It causes water dilution, lowered sensitivity, and lowersthe resistance to further water penetration. Salts may be washed out andparticles of sensitizer materials become separated. These difiicultiesare more or less proportional to the amount of air pumped with theslurry. It is obvious that these conditions may result in a completefailure to detonate, and in any case will result in a substantial lossof power in the explosion. Aeration of this type due to cavitation atthe pump has often been a serious problem in pumping slurries in thepast. One aspect of the present invention provides a very satisfactorysolution.

The pumping rate of any pump varies with the output pressure. Becauseslurry is pumped through a long fiexible hose which is moved about undermany varying conditions, the output pressure may vary constantly andconsiderably. While there are many obvious ways to maintain the rateindependent of pressure, the present inventors found it quitesatisfactory to maintain a pumping rate higher than necessary under thehighest expected pumping pressure, and by passing or recycling more orless of the slurry from the output back into the input as the occasiondemands which avoids pumping air to the delivery line.

It is desirable, and essential in fact, to prevent all unnecessarymechanical mixing of the slurry with water in the borehole. Since suchmixing tends to dilute the slurry and to cause it to break down, andpossibly fail, or at least greatly reduce its blasting strength, it isimportant to so handle the slurry that it is introduced first right atthe bottom of the borehole. It should be fed at all times so far aspracticable by pumping it to a point below the slurry-water interface.This is especially true in boreholes which contain water in quantity.That is to say that if there is water standing in a borehole, to anyappreciable depth, or if water is flowing in or through it, theexplosive material should be introduced below or under the Water ascompletely as possible. Starting at the bottom of the borehole, or asnear the bottom as practicable, the explosive composition should beforced into the hole below or under the standing or flowing water.Thereafter, it should continually be pumped to a hose outlet point whichis below the lower water surface in such a manner as to raise the watersmoothly with piston-like displacement and with minimum agitation of thewater above the slurry, always avoiding intermixing of water with theslurry as far as possible. This means that the end of the conduit orhose through which the slurry is introduced into the borehole should, asfar as practicable, be kept below the water-slurry interface. Of course,when the material is first introduced there is no water-slurryinterface, but the blasting material should first be introduced right atthe bottom of the borehole, or as near thereto as possible.

Since the slurry preferably is denser than the water, and especially ifwater is present in quantity, the slurry will sink immediately to thebottom of the hole causing the water to rise above it. In any case,mixture of the explosive composition with water should be minimized. Theblasting gels and slurries commonly used tend to adhere to the outerhose surface, making it messy or slippery and hard to handle if coveredto any great length. Hence, it is not desirable to continue pumping orslurry delivery with the hose end at the bottom of the hole. Also, thepressure requirements may increase unduly if the hose is not raised asthe hole is filled. One aspect of the invention is to avoid thesedifficulties. To do this, preferably the hose is withdrawn from theborehole at substantially the same rate as the slurry is filled into theborehole. By this, only a small length of hose, say one to three feet,is actually immersed at any time in the slurry. As the slurry rises to aheight of say 5, 10, 15, 20 or more feet, only the terminal foot or twoof the hose then becomes coated with the viscous slurry. This makes iteasier to handle the hose since the viscous gel-like materials are oftenquite difiicult to remove from the hose, in addition to making it veryslippery or messy to handle.

The preferred procedure then is to start pumping the slurry as near aspnactical at the bottom of the hole, delivering it as far as practicablein such a way that the water is merely raised above the slurry, and notsubstantially intermixed therewith. While it is possible to continuepumping with the end of the hose at the bottom of the hole, forcing theslurry to rise above the outlet of the hose to a distance of a number offeet and lifting the water above that, this procedure is not thepreferred one. Not only will a substantial length of hose becomecontaminated but the load on the pump and on the hose may be greatlyincreased, particularly with denser slurries. The hose is preferablyequipped with a guard over the end so that it will not be jammed intocrushed rock or other debris which might plug the hose end or causedifliculty in pumping. With the hose end near the bottom of the hole,pumping is started in such a manner as to force the slurry to the bottomof the hole and raise the water above it. It will be understood that theterm pumping, as here used, includes forcing the slurry through the hoseor other delivery tube by any source of fluid pressure. As pumpingcontinues, the slurry rises. The hose then is withdrawn, in thepreferred procedure, at more or less the same rate as the hole isfilled. Thus, the column of slurry grows, with a rising interfacebetween slurry and water. In this way, only a foot or two of hose isnormally actually riding in the slurry, no matter how high the explosivematerial eventually rises in the borehole.

As is known in the art, it is sometimes desirable to place explosives ofhigh explosive energy at the bottom of a borehole where more energy isrequired and to place less expensive explosives, with lower energy orexplosive density in the higher and top portions of the borehole wherethere is less burden. This desinable change of composition of the slurrymixture with position in the borehole can be accomplished in themixer-type pump operation by simply changing the rate of introducing thevarious ingredients or by changing one or more of the ingredients whichare mixed and pumped together. This procedure has great advantages inblasting operations where a more powerful load is needed at the bottomof a borehole, but a less expensive load is satisfactory for the upperpart of the charge. According to the present invention, this change ofcomposition as a function of position in the borehole can be madecontinuously, with the preferred mixer-type pump operation.

The invention will be further understood by reference to a specificembodiment and also to the accompanying drawings which illustrate notonly some details of the method described generally above, but alsoillustrate certain equipment aspects which are of assistance incontrolling the borehole filling operation. While reference has beenmade above to filling of boreholes which contain water, it will beapparent that at least some of the advantages of the invention applywhen the holes are dry.

Referring to the drawings, FIGS. 1A, 1B and 1C rep resentdiagrammatically boreholes in rock which contain some water and are tobe filled with a pumpable explosive. The various figures show differentstages of filling.

FIG. 2 shows diagrammatically a pumping system which includes a hosehandling and control mechanism.

FIG. 3 is an elevation at another angle of the hose handling and controlmechanism of FIG. 2.

FIG. 4 is a perspective view of the mechanism of FIG. 3, showing certainother parts and omitting some elements.

FIG. 5 is a graphical representation of thickening rates on typicalcompositions.

Referring first to FIGS. 1A, 1B and 1C, FIGURE 1A shows a typicalborehole 10 which may be, say, from about 6 to 10 inches or more indiameter, and of considerable depth. The hole will be ten feet or moredeep in many cases, and sometimes as much as forty or fifty feet ormore. This hole is shown a containing a substantial amount of water,indicated at 11. Such water may come from natural ground waters or itmay have been introduced in the process of boring the hole, since wateris frequently used in forming boreholes for blasting, especially in hotjet drilling. In this case, a delivery hose 13 which is of suitablediameter say 1 /2 to 2 /2 inches or so, is shown as having been insertedto or very nearly to the bottom of the borehole. The hose is equippedwith a guard or screen 15 at the bottom end, in the form of a light openframework of metal attached to the terminal end of the hose in anysuitable manner. The purpose of this guard or grid-like screen is toprevent the hose being rammed into a mass of rock or other materialwhich might clog it. In the position shown in FIG. 1A, pumping or otherforced delivery may be started, the flowing material coming out of theend of the hose as indicated by the small arrows at the bottom. Thus,the blasting material is immediately pumped to the bottom of theborehole with a minimum of mixing with borehole Water.

Referring to FIG. 1B, as the borehole begins to fill with the slurry 17,which is more dense than the water 11, the interface 19 between theslurry and the water rises and the upper surface of the water 21 willrise also unless the water can flow back into the formation, whichsometimes happens. Where there is considerable Water, it may overflowthe hole as the slurry is pumped in to replace it. In any case, as longas there is water above the slurry, excessive mixing of water intoslurry, or vice versa, should be avoided. Hence, as far as possible, theend of the hose 13 is at all times kept beneath the slurry and waterinterface.

In FIG. 1C the operation is continued further, with slurry 17 fillingthe borehole to a substantial height. As shown, and as is frequentlydesirable, a different slurry mix 27 may be introduced after the firstslurry mix 17 reaches a desired height, eg as indicated at 29. In thiscase, while mixing of slurry at the pump end is continued, theingredients are simply changed, either in proportions or kind or both,so that a slurry or gel 27 continues to fill the borehole and to pushthe water above it. The slurry-water interface 19 is at all times keptabove the outlet of the hose 13 after enough slurry has been fed tocover it. The extent or length to which the lower end of the hose isheld below the interface between water and slurry or gel should not beexcessive for reasons pointed out above, but otherwise it is notparticularly important, as long as the hose end is low enough that thereis not excessive turbulence and intermixing of slurry and water at theinterface between the Water and the gel. As the hole is filled, the hoseis retracted, preferably so that its outlet end will not be so low as toimpose heavy resistance to flow on the pump system or on the hoseitself. This also avoids contamination of a substantial length of thehose with slurry and, with water above the slurry, the hose can befairly clean when the hole has been filled and the hose withdrawn.

The procedure shown in FIG. 10 may be continued as far as needed and thecomposition of the gel or slurry '3 may be changed more than once, or itcan be changed gradually over a continuing period of time, if desirable.In all cases the hose is preferably withdrawn at about the rate at whichthe hole is filled, preferably continuously at a rate more or less equalto the rate of filling, to prevent excessive contamination of the hoseand also to reduce excessive back pressure on the pump. It may bewithdrawn intermittently, in small increments, in some cases if desired.A very thick slurry and a long hose can cause considerable flowresistance at the pump and in some cases could possibly result in actualbursting of the hose, not to mention the other difiiculties in handlingand the dangers inherent in high pressure pumping in such an operation.

The hoses employed in this operation are frequently long and quiteheavy. They should be built of sufiicient body to withstand substantialpressures. Therefore, it is frequently difficult to handle themmanually. For this reason, a hose control apparatus, as illustrated inthe lower part of FIG. 2 and H68. 3 and 4, facilitates the control andhandling of the hose.

This apparatus comprises a powered hose driving reel or drum 51, FIG. 2,mounted on an axle 53 supported in a suitable framework 55 mounted onlegs 57. One or more idler wheels, preferably two wheels 59, 61, aremounted in a movable auxiliary framework including a bar 63 and lever63a in such a way that they can be brought to bear frictionally whendesired against the hose which passes over the reel 51. In this waytraction can be applied to the hose to keep it in driving engagementwith the drum i. Reel 51, FIG. 4, is preferably driven by a suitableprime mover, e.g. a constant or a variable speed motor 65, through asuitable speed reduction device 67 which may include a drive belt 69passing over a pulley 71 which is connected in driving engagement withthe drum or reel 51. Drive belt 69 preferably is of the timing type. Thedrive itself may be variable in speed ratio. The arrangement is suchthat a selectively variable speed may be imparted to the drive of thereel under control of the operator. The operator can cause the reel toturn at the desired hose-raising rate at which the borehole is beingfilled.

In a typical pumping system, a combination of wet and dry ingredientsare fed into a hopper 80 from suitable sources, e.g. a bin of drymaterial or several bins of such, and a tank of liquid. The liquid isusually an aqueous solution of an oxidizer salt such as ammoniumnitrate, sodium nitrate or combinations of the two. It may also includeperchlorates or other oxidizers and fuels, e.g. glycols and the like andit may contain a small amount of thickener. The liquid material ispreferably introduced in such a way as to minimize contamination of thefunnel 89. It may be introduced into a lower funnel element 21 below anedge or flange of funnel 80 to minimize splashing or sloshing into theupper funnel. The dry ingredients flow down the funnel elements 80, 81to a mixing chamber 82 where a suitable mixer, e.g. of an impeller type84, driven by a rotary shaft 86, suitably mixes the wet and drymaterials together in a smooth or reasonably homogeneous blend. it willbe understood that some, and sometimes all, of the dry materials are notsoluble in the liquid. These dry ingredients may comprisenon-explosives, e.g. aluminum powder, granular oxidizing salts such asinorganic nitrates, etc., sulfur, finely divided coal, gilsonite, orthey may comprise explosive materials such as solid particles of TNT,smokeless powder, etc. of appropriate particle size, as is now wellknown in the art. The ingredients are preferably maintained at a levelto provide a hydrostatic head on the pump as indicated at 87, FIGURE 2.A level indicator 89 shows the head.

The mixed materials pass on into a pump shown diagrammatically at 88,preferably of the positive displacement type. The slurry is passed intoline 90 and to a 3-way adjustable valve 92. Two ordinary valves mayreplace valve 92, if desired. From the latter, the stream may berecycled through a line 94, or delivered through hose f3,

or divided so that part flows through both. The material flows throughhose 13 to the bottom of a borehole as previously described. The pumphas greater capacity than is normally required but the recyclesubstantially revents cavitating or pumping air and the valve 92, or twosimple adjustable valves, may be set to recycle any desired part of thestream through the by-pass line 94.

Returning to a description of the hose handling mechanism, means areprovided for applying frictional pressure to the hose as it rides overthe reel 51, through the idler wheels 59 and 61. These wheels aremounted on auxiliary frames which include a member 63. A pivoted lever110, mounted on a suitable pivotal support 112, has an adjustabletoothed rack 114 with an engaging tooth H8 and control elements 116.This lever is used to adjust the position of the idler wheels withrespect to the drum or wheel 51. A coil spring 12ft, FIG. 4, keeps thetooth or detent 118 in engagement with the rack 114 except when the handgrip control elements 116 is operated to release the detent, as isconventional with levers of this type.

When the parts are in the full line position of FIG. 3, the hose is notbeing frictionally gripped, but the reel is arranged to be driven at aspeed which may be controlled as desired, as previously described. If itis now desired to retract the hose, the speed of the reel is set toapproximate the speed at which the hole is being filled. This can bejudged rather accurately after a little experience. Then the lever 1163is shifted, e.g. to the dotted line position, FIG. 3, to bring thewheels 59 and 61 into frictional engagement with the hose. This causesthe rotating reel to pull the hose up out of the hole. By carefulcontrol of the withdrawal of the hose in the borehole, only a shortlength becomes immersed in the slurry. Any water above the slurry-waterinterface tends to keep the hose clean so that it comes out relativelyuncontaminated with the slurry. Of course a short length at the end ofthe hose may be quite heavily coated with slurry, especially when thickviscous materials are being used. The drive mechanism is preferably madereversible so that it may be used to lay out hose as well as to draw itin, if desired.

The assembly of FIGS. 3 and 4 is relatively light in weight and can becarried if desired or rolled on wheels (not shown), from hole to hole asthe hose is inserted and withdrawn for each filling operation.

Instead of mounting a drive motor on this assembly, the speed reductionunit 67 may be driven advantageously through a flexible shaft from aprime mover, e.g. electric motor or a power take-off at the pump truck.A suitable connection is shown for this purpose at 130, FIG. 4. Thiseliminates the necessity for a separate motor on the hose withdrawalassembly and thereby reduces the weight of the hose handling device.This is advantageous because the terrain on which blasting operationsare conducted is often very rough and difiicult.

In some operations it may be necessary to reel in or reel out quite asubstantial length of hose. For example, in cases where the hole is verydeep, and in cases where it is not possible to place the hose liftingunit near the borehole, but it must be at some higher elevation, asubstantial load of hose may be involved.

The use of the hose handling equipment of FIGS. 2 to 4 greatlyfacilitates the borehole filling operation, not only in situations wherethe hose is too heavy for one man to handle or its length is great, asin the instances just mentioned, but even where the hose could behandled manually. Better control is maintained. It has been found inexperience, furthermore, that mine operators generally dislike to handlethe hose manually, sometimes because of its heavy weight and alsobecause of the inconvenience, poor footing, etc., at places where thehose is being used.

It is desirable to lift the hose fairly directly, i.e. vertically, fromthe borehole and not to drag it over or around the sharp edges of rockwhere the hole is formed. Where this is not possible, a roller or otherfriction reducing and hose protecting guide can be placed at the edge ofthe borehole so that the hose can be pulled out from a lateral directionand not from directly above without damage or excessive work. Theadvantages of the method and apparatus described above still apply.

Obviously a reeling device may be provided in some cases on the truck orpumper unit itself. The pump truck, however, is likely to be at asubstantial lateral distance from the borehole, so the use of a reel atthe truck often involves pulling the hose over jagged rock at theentrance to the borehole. Frequently this damages the hose. In such acase it is useful again to employ a roller or smooth buffer guide offriction-reducing type at the entrance to the borehole. Such devicesform no part of the present invention, but are well known in the art ofhose handling. It is preferred, however, where feasible, to lower andlift the hose vertically or as nearly so as convenient. The apparatusshown has real advantages for this purpose.

The whole pumping and hose handling system just described facilitatesthe orderly filling of boreholes. It gives assurance that the explosivein the hole, particularly in a water filled hole, will be in goodcondition for the blasting operation. It minimizes the mixing of airand/ or water into the explosive. It gives insurance that the productwill be homogenous, that the borehole will be thoroughly filled frombottom to the desired top level, all without excessive quantities ofwater or air or other foreign material diluting the mixture and settingup conditions that may result in blasting failure.

A test explosion was carried out on a mine location where there were 50foot benches at an elevation above 6,000 feet above sea level. A 9 inchdrill hole, 56 /2 feet deep containing 35 feet of water in the bottom ofthe hole, was selected for this particular test.

Slurry was pumped at the rate of 400 lbs. per minute. It was desired tochange the mix during pumping putting a high energy mix A at the bottomof the hole and a lower energy and less expensive mix B in the upperpart of the hole. It was estimated that the hole would contain about1,000 lbs. of explosives so it was planned to put 400 lbs. of a mix Aand 600 lbs. of the less expensive mix B in the hole. The hose consistedof a 50-foot length of 2-inch (inside diameter) hose, followed by 50feet of 1 /2 inch (inside diameter) hose. The first 50 feet presentsless friction to flow and the last 50 feet is more slender and easier tohandle.

In this particular test, the hose operator placed the end of the hose atthe bottom of the hole and signaled to the pump truck operator whoturned on the controls for the mixing and pumping operation. After oneminute of filling with mix A, the mechanism automatically switched tomixing and pumping the lower grade explosive B. Within about 15 secondsafter the pump truck operator signaled for the change in mix, the hoseman retracted the hose about 5 feet up the hole, as indicated bydistance marks on the hose itself. At a pumping rate of 400 lbs. perminute, as calculated, it would take about 14 seconds for the interfacebetween mix A and mix B to traverse the 50 feet of 2-inch hose and 8seconds additional to traverse the 50 feet of 1% inch hose, a total of22 seconds. The bottom of the hose was thereafter raised in incrementsof about 5 feet by the operator, in such a way that the open end of thehose always remained below the slurry-water interface.

The explosive raised 23 feet in the hole as about 43 lbs. per foot wereinjected into the borehole. In this particular hole the water was raisedjust to the top of the hole as it was displaced upward by the denserexplosive. Apparently a small amount of the rising water escaped throughside fissures, etc.

Immediately after pumping ceased, the hose was withdrawn, completelyfrom the hole. About 3 minutes later,

borehole cuttings were poured into the hole as stemming, replacing alarge part of the water which then overflowed the hole.

In this operation the pumping pressure, recorded by a gauge at the pumptruck, started at about 25 lbs. per square inch. It later reduced toabout 15 lbs. per square inch as the slurry started to fill the bottomof the hole. The pumping pressure increased somewhat, to about 20 lbs.per square inch by the time the last slurry was put into the hole. Theremay have been some siphoning action at the bottom of the hole after theslurry stream got moving through the hose. It would be expected thatthis siphoning effect would decrease as the hole became filled,requiring some increase in pumping pressure. Apparently this is whatoccured.

The slurry as mixed had an initial temperature of about 56 C., thesolution temperature being 65 C. It had a density in the case of mix Aof about 1.33 and about 1.27 for mix B. Both compositions of coursecooled rapidly in the borehole and this assisted in thickening themquickly. They also contained thickening agents, a small amount of guargum and a larger amount of tapioca flour, in both mixes. Both containeda small amount of very fine aluminum and some coarser aluminum powder.The total aluminum content was greater in mix A than in mix B.

The viscosity of the materials was determined by a special penetrometerwhich measures the depth of a conical weight pressing down into theslurry. The first slurry had a penetration of 237, indicating 23.7 mm.,and the second of 288 indicating 28.8 mm. As shown in FIG. 5, thethickening rate varied somewhat but in both cases was such as to preventseparation of the solid particles from the slurry by the time it becamequiescent in the borehole.

The apparatus of FIGS. 3 and 4 may be modified and made quite automaticby placing at or near the end of the hose a. condition sensing means, inthe form of elements or a device which will control the hose liftingrate. This sensing device may be a single unit or multiple elements.These may be either of a pressure type, e.g. one which senses the amountof slurry and water above the end of the hose, or of a temperaturesensitive type. The latter is usually preferred. Since the slurryusually has a different temperature from that of the borehole, or of thewater in the borehole, advantage may be taken of this temperaturedifferential. An element sensitive to temperature is designed thereforeto control the drive rate of the means which pulls the hose out of theborehole. One temperature sensitive device is indicated onlydiagrammatically at 140, FIG. 2. This device is of a conventional typebut designed to signal a control element in the speed control at thehose lift mechanism. If the hose is being withdrawn too rapidly, theelement gets up into the water, is cooled, or changed in temperature,and gives a signal through line 141 to control mechanism 142, FIG. 2, tothe lift mechanism to slow down the withdrawal operation. Thetemperature sensitive element 140 may be located preferably at theinterface between water and slurry. In this case, with about one tothree feet of hose below the interface 19, the temperature sensitiveelement being normally located on the hose and at the interface 19between water and gel, the lifting rate will be maintained automaticallyby the temperature element. This mechanism may be used also to shut offthe hose lift drive motor when the hole is filled. Since some slurryusually will adhere to the hose at the junction, in water-filledboreholes, a definite time interval may be required for slurry to bewashed off as the hose is pulled up through the water. The slurry lefton the hose thus should either be washed off to expose the termocoupleor at least it should be sufficiently cooled to de-energize a switchingrelay in the drive mechanism at the appropriate time. The latter is notshown, being obvious to those skilled in the art. In this case the endof hose-to-junction distance should be adequate to prevent the hose endfrom being pulled com- 11 pletely out of the slurry before the retractoror lifter motor is stop ed.

After the end of the hose or conduit is covered or buried in the slurry,it is preferably kept continuously below the top of the slurry, eventhough the hose is being progressively retracted, intermittently orcontinuously, as the hole is filled. If during any stage of loading theborehole, there is no water, or if the rising water in the boreholeshould flow off into crevices. which sometimes occurs, to thereby bringthe thermocouple or detector point out into air instead of water, thecooling rate of the junction might be too slow to stop the motor beforethe hose is pulled out of the slurry. This is not serious, however. Ifwater is absent in the hole, there is no problem of mixing water intothe slurry. There may still be a possibility of having too much air inthe slurry, but this can be avoided by the operator giving reasonableattention to the hose.

In many operations, the borehole is essentially cylindrical and isfairly uniform in dimensions. In the case of jet pierced holes, however,where diameter is not uniform and where it may vary from point to pointin the hole, it may be necessary to determine by experience the likelyminimum volume of any hole that is to be loaded. The hose or conduitretraction rate in such case should be estimated on the maximum possibleslurry rise rate, which is an inverse function of hole diameter. Hoseretraction from holes of larger volume preferably should be handled inthe manner already described. The constantly varying effective volumeper unit length of jet-pierced holes may result in some fluctuations inthe slurry rise rate. However, these generally will average out and notcause excessive stopping and starting of the retractor motor whichoperates the hose lifting operation. Experience will usually help theoperator to keep the hose lift at the optimum rate.

Obviously more refined controls may be used if desired. A plurality ofthermocouples may be employed, operating at successively differenttemperatures and depending on ground temperature variations at variousdepths, as well as for a better control of the hose withdrawal rate.Suitable circuits for such controls may readily be designed by those whoare skilled in the art. A signal device also may be incorporated on thehose lifting device, as indicated diagrammatically at 143, FIG. 1, toindicate to the operator whenever any unusual or abnormal situation isarising at the discharge end of the hose. There may, for example, be alarge fissure or side opening in the borehole not known to the operator,where excessive quantities of slurry might be pumped and lost or wastedbefore the operator knows what is going on. Such conditions can beindicated on the device 143 by use of simple sensing means, sensitive torate of slurry rise, for example, located on the hose. The signal may beof any conventional kind, e.g. either a dial or a light, or a buzzer,indicating abnormal pressure or temperature conditions at the end of thehose.

The use of dual sensing elements 151 and 152. one normally below and onenormally above the interface point on the hose (see FIG. 18) with acommunication line 153 to a control box MBA. FIG. 4. can be made insteadof the single control Mil described above. in this case if the hoseretraction rate is too slow, the upper detector 15 set for watertemperature, senses the warmer slurry as it sinks into it and signalsthe variable speed drive controller 142A to speed up the drive rate andpull the hose up faster. Conversely, if the rate is too rapid, the lowersensing element 152, preset for normal slurry temperature, will riseinto the water, sense its different temperature, and signal for a slowerwithdrawal rate.

As is well known in the art, plastic socks or hole liners may beinserted first into the borehole and then filled to the generalexclusion of water or in such a way as to prevent serious loss of theexplosive slurry in side holes and fissures. These socks frequently maybe punctured, since they are commonly made of thin plastic material andare subject to dragging over jagged rock edges. Thus they may notprevent completely the intrusion of water. However, they will generallyexclude large losses of explosive material.

It will be obvious to those skilled in the art that other variations maybe made in the method and also in the apparatus of this invention. it isintended by the claims which follow to cover all such variations andmodifications as come within the proper broad scope of the invention asindicated by the prior art.

What is claimed is:

l. A method of filling a fiowable explosive slurry which is denser thanwater into a borehole containing water, which comprises the steps, incombination, of first introducing the slurry from a forcing stationthrough a laterally unconfined conduit which extends substantially toand has its outlet adjacent the bottom of the borehole, forcinginitially a sufiicient quantity of slurry to flow to fill the bottom ofthe hole and to lift the water above the outlet end of the conduitthereby to cover or bury the end of the conduit in slurry, andthereafter withdrawing the conduit upwardly from the borehole whilecontinuing to force the slurry into the borehole. and coordinating thepumping rate and the conduit withdrawal rate so as to keep the outletend of the conduit at a point substantially always below the top surfaceof the slurry, thereby to prevent excessive intermixture of water andslurry.

2. Process according to claim 1 wherein the end of the conduit is keptsubmerged in slurry substantially throughout the forcing operation afterits end is first buried in slurry but is progressively lifted enough, asthe hole is filled, to substantially minimize back pressure at theforcing station.

3. Process according to claim 1. wherein a delayed actionwater-resistant thickening agent is added to the slurry essentially atthe forcing station, said agent being timed to become sufficientlyeffective by the time the slurry reaches the borehole to assist inpreventing water leaching of the slurry.

4. Process according to claim 1 wherein occluded air passing through theconduit with the slurry is limited to proportions too small to causesubstantial mixing at the water-slurry interface or to produce asubstantial air gap in the explosive slurry column in the borehole.

5. Process according to claim 1 wherein a delayed action thickeningagent is added to the slurry essentially at the forcing station, saidagent being timed to become sufficiently effective by the time theslurry reaches the borehole to substantially impart water resistance andprevent gravitational segregation of suspended particles from the slurryon standing in the borehole.

6. Process according to claim 1 wherein the slurry includes both agelling agent and a cross-linking agent for the gelling agent.

7. Process according to claim 6 wherein the gelling agent is precookedtapioca starch.

3. Process according to claim 6 wherein the cross-linking agent is analkali metal dichromate.

9. Process according to claim 6 wherein borehole conditions are sensedand the sensation is used to control the withdrawal rate of the deliveryconduit.

ll Apparatus for controlling lifting a slurry delivery hose in awater-filled borehole which comprises a driven drum over which the hosepasses, adjustable means movable towards and away from said drum forselectively applying driving frictional pressure to the hose in relationto the driven drum, and means for varying the rate at which the drum isdriven so that the hose can be controllably withdrawn at a rate notsubstantially greater than the rate at which the borehole is filled.

ill. Apparatus according to claim 13 which includes a sensing elementfor determining the position of the hose outlet with respect to theupper surface of the slurry in the borehole, and means for affecting theoperation of said References Cited UNITED STATES PATENTS Woodbridge102-12 Farris 166-21 Hradel et a1. 102-23 Moor 141263 X Barco et a1.86-20 BENJAMIN A. BORCHELT, Primary Examiner. P. A. SHANLEY, AssistantExaminer.

